Hydrochloroquine, also known as hydroxychloroquine (Plaquenil), was originally approved by the FDA for treatment of malaria in 1955. It works by decreasing certain cell signaling processes involved in inflammatory responses, which is why it is also effective in treating inflammation caused by autoimmune conditions. Hydrochloroquine is available by prescription to be taken orally, in tablet form, over several weeks. The most common side effects associated with hydrochloroquine are mild nausea and stomach cramps with mild diarrhea. Other side effects associated with this medication can include irritability, headache, weakness, hair lightening or loss, stomach upset, nausea, dizziness, muscle pain, rash and itching.